Hybrid Hose Reinforcements

ABSTRACT

A crush resistant hose comprises a plurality of layers ( 12, 14, 16, 18, 20 ) comprising a reinforcing carcass formed from a mixture of multifilament fibres ( 30 ) including at least one of polyester, aramide, nylon and rayon.

The present invention relates to hoses, and in particular to reinforcinglayers in large bore crush resistant hoses.

Large bore hoses are used, for example, for transporting large volumesof oil, such as in the loading and unloading of oil tankers. The hosesare exposed to arduous conditions and subjected to high loads. Largebore crush resistant hoses are therefore made up of a number of layers,typically including an inner lining, a reinforcing carcass, crushresistant wires and a cover layer. Each of these layers can be made upof a number of separate sub-layers.

The reinforcing layer is typically made up of cord or yarn that iseither simply wound round the hose or woven into a fabric. Theproperties of the cord need to be selected to give the hose its requiredphysical strength. It is known to make the fabric or cord of thereinforcing layer from Nylon, Rayon, polyester, or aramides such asKevlar™ or Twaron™. However, these materials have varying physicalproperties with their own advantages and disadvantages and do not alwaysprovide the best properties required. Large bore crush resistant hosessuch as those described are used in dynamic applications and it istherefore essential that the material is able to withstand fatigue. Itis known to make the fabric or cord from monofilament yarn, staplefilament yarn or a combination of any of these. However, the physicalproperties of these known fabrics do not display the level of resistanceto fatigue that is required for a crush resistant hose used in dynamicapplications.

Accordingly the present invention provides a crush resistant hosecomprising a plurality of layers, one of the layers comprising areinforcing carcass formed from cord made from a mixture ofmultifilament fibres including at least one of polyester, aramide, nylonand rayon. Using such a hybrid material allows the best physicalproperties of each material to be selected and combined, allowing theconstruction of a significantly lighter and stronger hose. The use ofonly multifilament yarn provides a material that is both flexible andstrong and displays optimal fatigue properties. The multifilament yarnspreferably have at least 100 filaments in each yarn. Each filamentpreferably has a length of the same order as the yarn, preferably ofsubstantially the same length of the yarn.

Preferably, the mixture of fibres comprises two of polyester, aramide,nylon and rayon and may comprise different proportions of each material.Most preferably, the cord is formed from a mixture of multifilamentfibres of at least one polyester and at least one aramide.

The mixture of fibres may comprise a higher proportion of aramide thanof polyester. Preferably the mixture comprises a ratio of 2 plies ofaramide to one ply of polyester. However, it may comprise a ratio ofbetween 1:1 and 4:1, preferably between 1.5:1 and 3:1. This mixture ofpolyester and aramide fibres increases the strength of the reinforcinglayer.

The reinforcing layer may be formed from cord comprising a plurality ofthe fibres. Preferably, the cords are woven into fabric and may becoated with rubber before being applied to the hose. The cords may lieat an angle α to the longitudinal axis of the hose. The angle α may bebetween 30° and 55° with the lower limit more preferably being 35° andthe upper limit more preferably 50°, still more preferably 45°, and ismost preferably approximately 40°. The woven fabric creates areinforcing layer capable of withstanding the arduous conditions andhigh loads experienced by the hose. Alternatively, the cord may be woundaround the hose without being woven into a fabric.

The cord may comprise 2 plies of aramide and 1 ply of polyester twistedtogether. Preferably, the plies are twisted at approximately 190 turnsper metre. Each aramide ply may comprise 3 plies of yarn, which may betwisted together at approximately 190 turns per metre. Each polyesterply may also comprise 3 plies of yarn, which again may be twisted atabout 190 turns per metre. Alternatively, each ply may comprise amixture of plies of different materials, for example two of aramide yarnand one of polyester yarn. Again, other ratios may be used, for example3:1, 3:2, 4:1, or 4:3.

Any suitable aramides and polyesters may be used. However, the mostpreferable aramide is Twaron™ 1008 and the most preferable polyester isDiolen™ 164S.

Preferred embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings inwhich:

FIG. 1 is a section through a wall of a hose according to an embodimentof the invention;

FIG. 2 shows the make-up of a reinforcing layer of the hose of FIG. 1;

FIG. 3 is a table showing the physical properties of the hybrids andother materials; and

FIG. 4 shows the make-up of a further reinforcing layer of the hose ofFIG. 1.

Referring to FIG. 1, a crush resistant hose 10 according to anembodiment of the invention comprises a number of layers. Starting fromthe inside of the hose and working outwards, these layers include alining 12, an inner reinforcing layer 14, an outer reinforcing layer 16,a crush resistant layer 18, and a cover 20. The crush resistant layer 18comprises one or more separate layers of crush resistant wire 22, inthis case two, and the cover 20 comprises two cover layers 24, 26. Allof the layers apart from the reinforcing layers are conventional and canbe produced so as to be suitable for any specific application.

The reinforcing layers 14, 16 are formed from a mixture of polyester andaramide multifilament fibres. Referring to FIG. 2, the inner reinforcinglayer is made from cords 28 woven into a fabric 30. Although the cords28 are shown spaced apart in a loose weave for clarity, they are inpractice woven closely together to form the fabric. In this embodiment,the fabric 30 is coated in rubber before being applied to the hose. Thecords 28 of the fabric lie at an angle α to the longitudinal axis of thehose 10, an angle of approximately 40° in this embodiment. The angle αcontrols the physical properties of the hose and is chosen so as tosatisfy as many of the design requirements as possible. The angle α willvary for different hose designs and generally lies in the range 350 to55°.

In this embodiment, each cord 28 is made up of 2 plies of the aramideTwaron™ 1008 and one ply of polyester Diolen™ 164S. The three plies aretwisted together at approximately 190 turns per metre to form the cord28. This cord 28 typically has a thickness of approximately 1.55 mm.Each Twaron™ ply is made up of three plies of multifilament 1680 decitexyarn twisted at approximately 190 turns per metre. Each Polyester ply ismade up of three plies of multifilament 1670 decitex yarn, also twistedat approximately 190 turns per metre. The use of multifilament yarninstead of monofilament yarn, staple filament yarn or a combination ofthese has been found to produce a material that displays improvedresistance to fatigue. Multifilament yarns comprise hundreds ofcontinuous individual filaments together in one yarn. For example, atypical 1670 decitex Twaron™ yarn comprises approximately 1000 filamentseach with a diameter of 12 microns. Multifilament yarns are veryflexible and strong and display optimal bending fatigue and tensilefatigue properties compared to monofilaments, which are much stiffer anddisplay poor fatigue properties. Staple filament yarn comprises shortlengths of filament wrapped around each other, transferring load alongthe filament through the friction between the filaments. Staple filamentyarn therefore lacks the strength found in continuous multifilamentyarn.

Referring to FIG. 3, tests were carried out on the different propertiesof three slightly different samples of the hybrid cord. The table alsoshows the results for control samples of Twaron, Rayon and Nylon. Eachof the three hybrids has a slightly different number of turns per metre,the single twist of the Twaron™ or polyester of hybrid 1 being about 183tpm, 190 tpm for hybrid 2 and 175 tpm for hybrid 3. The number of turnsper metre of the 3 plies in the cord, the cord twist, is about 179 tpmfor hybrid 1, 180 tpm for hybrid 2 and 163 tpm for hybrid 3. The threesamples also have a slightly different cord thickness. This isapproximately 1.55 mm for hybrids 1 and 3 and 1.59 mm for hybrid 2. Thelinear density also varies between the three hybrid samples, the valuesbeing approximately 17679 dtex, 18430 dtex and 17740 dtex respectively.These values are similar to the linear density of 17670 dtex for theTwaron™ control sample but are much greater than the value of 8250 dtexfor the rayon control and smaller than the value of 25380 dtex for thenylon control.

It can be seen from the results that the breaking strength (N) of eachof these hybrids is considerably greater than that of the rayon controland is also greater than the nylon control. The breaking strengths ofthe three hybrids are 1845N, 1620N and 1894N respectively compared to abreaking strength of 293.8N for the rayon control. Only the 100% Twaron™sample has a greater breaking strength of 2822N. The breaking tenacityof the hybrids is also much greater that of the rayon control. Thehybrids have a breaking tenacity of 1087 mN/tex, 932 mN/tex and 1115mN/tex respectively compared to a breaking tenacity of 372 mN/tex forthe rayon control. Again, it is only the 100% Twaron™ sample that has agreater breaking tenacity of 1664 mN/tex.

Another of the properties tested was the elongation at breaking point.This elongation was found to be 7.5%, 7.7% and 6.6% respectively for the3 hybrids. These compare to a lower value of 5.4% for the Twaron™control sample and the considerably higher values of 16.6% and 29.1% forthe rayon and nylon control samples. The chord modulus also differsbetween the three hybrids and the Twaron™, being 16.7 GPa, 15.4 GPa and19.4 GPa for the hybrids and a much higher value of 31.8 GPa for theTwaron™. The greater elongation at breaking point of the hybrid comparedto the Twaron™ control, along with its lower modulus, is one of the keyadvantages of the hybrid over the Twaron™. It enables the hybrid to loadshare better than the 100% Twaron™, an important factor whenconstructing thick hoses.

The hybrid fabric may also be coated in rubber before being applied tothe hose 10. The rubber coating further increases the strength of thefabric and therefore the durability of the hose 10 when exposed to highloads. The strap peel force, a standard adhesion test, was measured fortwo different types of rubber applied to each of the three hybrids. Forthe r838 rubber, the values of the strap peel force for the hybrids are258 N/cm², 258 N/cm² and 241 N/cm² respectively, which are very similarto 255 N/cm² for the Twaron™ and 240 N/cm² for the rayon. For the 5320rubber, the strap peel force values are 165 N/cm², 123 N/cm² and 185N/cm² for each of the hybrids, which are again similar to the value of176 N/cm² for the Twaron™ and 169 N/cm² for the rayon.

The T-adhesion was also measured for each of the samples. This is amethod of assessing the adhesion between rubber and cords and is thetest used by cord manufacturers. Several cords are moulded into a blockof rubber, the block being approximately 10 cm long and having a squaresection of approximately 1 cm. The block is built up in layers and thecords are laid onto the rubber at right angles to the block length as itis built up. The sample is then cured. The cords are pulled individuallyfrom the block and the force required to do this is measured. Cordsproject at one side to allow them to be pulled, and by 1 or 2 mm fromthe other edge of the block to ensure that they extend right through theblock giving a pull length of 10 mm. For the 5320 rubber, the values foreach of the three hybrids are 870N, 670N and 740N respectively, whichcompare to a value of 770N for the Twaron™ control and which are greaterthan the value of 284N for the rayon control. The values using 5320rubber are less than those obtained for the r838 rubber. This gavevalues of 1110N, 1160N and 1140N for the three hybrids, 1200N for theTwaron™ and 262N for the rayon.

These adhesion tests are important since the strength of the hosedepends on the ability of the fabric to bond with the rubber and theability of the rubber layers to bond with each other.

The strength retained after fatigue is another important property of thematerials. This is measured using the Akzo Nobel Flex Fatigue (AFF)test. A rubber strip approximately 25 mm wide is flexed around a spindleat a specific load. The rubber strip comprises two cord layers, theupper layer containing a material of very high modulus such as Twaron™and the lower cord layer containing the cords to be tested. The Twaron™layer carries almost the full tensile load because of its comparativelyhigh stiffness. The test cords of the bottom layer experience bending,deformation due to axial compression, and pressure from the upper cordlayer. Bending and deformation in the presence of this lateral pressurecauses degradation of the cord. After the strip has been flexed, thecords are carefully removed from the strip and the retained strength isdetermined using capstan clamps. In this case, r838 rubber was used andthe values were measured both in Newtons and as a percentage. Thepercentage is the ratio of the retained strength to the strength of theunflexed strip. The values obtained are 46%, 73% and 32% and 850N, 1190Nand 620N respectively for the three hybrids and are 32% and 910N for theTwaron™ and 12.7% and 37N for the rayon.

Overall, the strength of the fabric made with the hybrid cord isapproximately 4 times greater than the strength of the rayon fabricpreviously used. The 3 hybrid samples have a fabric strength of 962kN/m, 822 kN/m and 988 kN/m respectively compared to a fabric strengthof 235 kN/m for the rayon. Four layers of this rayon fabric cantherefore be replaced with one layer of the fabric woven from the hybridcord.

Referring to FIG. 4, in an alternative embodiment the reinforcing layer14 is formed from cords 28 that are wound round the lining layer 12.Although the cords are shown spaced apart for clarity, they are inpractice closely wound so as to form a substantially continuousreinforcing layer 14. The cord 28 is wound at an angle β relative to thelongitudinal axis of the hose 10 to provide the hose with the requiredproperties. The value of the angle β determines the physical propertiesof the hose and is therefore chosen to satisfy most of the designrequirements. As in the previous embodiment, the cord is formed from twoplies of the aramide Twaron™ 1008 and one ply of polyester Diolen™ 164Stwisted together. The Twaron ply is again made from three plies ofmultifilament 1680 decitex yarn and the polyester is made from threeplies of multifilament 1670 decitex yarn.

The embodiments described above are also applicable to the use ofsuitable aramides and polyesters other than Twaron™ 1008 and Diolen™164S.

The invention is not limited to cord formed from a mixture of polyesterand aramide fibres, but may also be formed from other combinations offibres such as nylon and polyester or nylon and aramide. The combinationand proportions of fibres used can be selected to obtain the requiredproperties of the cord since different combinations will providedifferent properties.

1. A crush resistant hose comprising a plurality of layers, one of thelayers comprising a reinforcing carcass formed from a mixture ofmultifilament fibers including at least one polyester and at least onearamide, wherein the mixture comprises a higher proportion of aramidethan of polyester.
 2. A hose according to claim 1 wherein the mixtureincludes plies of aramide and plies of polyester and the ratio of thenumber of plies of aramide to the number of plies of polyester is from1:1 to 4:1.
 3. A hose according to claim 2 wherein the mixture comprisesa ratio of from 1.5:1 to 3:1 plies of aramide to polyester.
 4. A hoseaccording to claim 3 wherein the mixture comprises a ratio of two pliesof aramide to one ply of polyester.
 5. A hose according to claim 1wherein the reinforcing layer is formed from cord comprising a pluralityof the fibers.
 6. A hose according to claim 5 wherein the reinforcinglayer comprises a fabric woven from the cords.
 7. A hose according toclaim 6 wherein the hose has a longitudinal axis and the cords of thefabric lie at an angle of from 30 degrees to 55 degrees to thelongitudinal axis.
 8. A hose according to claim 7 wherein the cords ofthe fabric are positioned at an angle of approximately 43 degrees to thelongitudinal axis.
 9. A hose according to claim 5 wherein thereinforcing layer comprises a lining layer and a cord wound around thelining layer to form a substantially continuous layer.
 10. (canceled)11. (canceled)
 12. A hose according to claim 5 wherein the cordcomprises two plies of aramide and one ply of polyester twistedtogether.
 13. A hose according to claim 12 wherein each aramide plycomprises three plies of twisted multifilament yarn.
 14. A hoseaccording to claim 12 wherein each polyester ply comprises three pliesof twisted multifilament yarn.
 15. A hose according to claim 12 whereineach ply comprises from 160 to 200 turns per meter.
 16. A hose accordingto claim 1 wherein the reinforcing layer is coated in rubber.
 17. A hoseaccording to claim 1 wherein the breaking tenacity of the mixture offibers is from 800 mN/tex to 1300 mN/tex.
 18. A hose according to claim1 wherein the elongation at break of the mixture of fibers is from 5.5percent to 13 percent.
 19. (canceled)